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The expression of glial fibrillary acidic protein (GFAP), vimentin, S-100 protein (S-100), HNK-1, myelin basic protein (MBP) and fibronectin was investigated immunohistochemically in 51 ethylnitrosourea (ENU)-induced neurinomas of the rat. Additionally, 90 transplantation tumors derived from ENU-induced neurinomas and the RN6 rat neurinoma cell clone were studied. Vimentin immunoreactivity was shown in 50/51 primary neurinomas and 60/90 transplantation tumors. In contrast, GFAP was expressed in only 23/51 primary tumors and in 5/90 transplantation tumors. In the RN6 neurinoma clone, vimentin and GFAP could be demonstrated both in vivo and in vitro. GFAP expression varied depending on the tumor localization, i.e., tumors of distal portions of peripheral nerves were more frequently GFAP positive than tumors of the spinal roots or of cranial nerves. The same tendency was observed for S-100. In the series of transplantation tumors S-100 and GFAP immunoreactivity decreased with increasing numbers of transplantation passages. Only individual cells in 5 primary tumors were HNK-1 positive and no MBP-immunoreactive cells were observed. Our results demonstrate that the expression of differentiation antigens in ENU-induced experimental neurinomas parallels the results reported for human neurinomas.

Brain tumors were induced in adult inbred Fischer rats (F-344) by systemic administration of N-methyl-N-nitrosourea mixed in the drinking water (pH 6,2). Four of these tumors, one pleomorphic glioma (78FR-G-219), two pleomorphic mixed gliomas (78FR-G-284, 78FR-G-344) and one grade I to II astrocytoma (78FR-G-299) were established in vitro and maintained as permanent cultures. The glial nature of all cell lines was ascertained by demonstrating the presence of the S-100 protein in the cultured cells. All cell lines grow as tumors when isografted in syngeneic animals. Glioma cells were conjugated with trinitrobenzene sulfonic acid (TNBS) under standard conditions. Syngeneic adult rats were immunized with TNBS-modified or unmodified irradiated glioma cells by s.c. inoculation of 1 X 10(6) cells on days 1,8 and 15. Two weeks later the animals received a s.c. booster of 5 X 10(6) native cells. Using the complement-dependent microcytotoxicity test glioma cytotoxic titers were measured 5, 6 and 7 weeks after the first immunization. The results indicated that trinitrophenylated glioma cells induced a cytotoxic antibody response against native glioma cells which was higher than that induced by untreated cells.

Purified McAbs (14AC1) of IgG2a isotype raised against an experimental rat glioma (79FR-G-41) were labeled with Na131I and used for in vivo imaging of glioma grafts by external body scintigraphy. Normal mouse 131I-IgG was applied as control for non-specific uptake of proteins in the tumor. Nude mice bearing glioma grafts were injected i.v. with 15 micrograms of the 131I-McAb or 131I-IgG with an activity of approximately 150 microCi. Scans obtained 30 min, 24, 48, 72, and 96 h after injecting the intact 131I-14AC1 antibody demonstrated enrichment of radioactivity in the tumors. The tumors were clearly visible 48 h after injection of 131I-labeled antibody. The time course experiments showed that the uptake of 131I-14AC1 antibody in the glioma grafts was the result of specific antigen binding. Intact antibody provided adequate tumor visualization in the scintigrams without background subtraction. Therefore, this technique appears promising for in vivo tumor detection and may offer the possibility of improvement in the evaluation of diagnostic and therapeutic approaches to human gliomas.

The expression of glial fibrillary acidic protein (GFAP) and vimentin was investigated immunohistochemically in 104 experimental gliomas induced by transplancental application of ethylnitrosourea (ENU) in CDF rats. Immunoreactivity for vimentin was prominent in many astrocytic tumor cells and especially in small glioma cells forming anaplastic medulloblastoma-like foci in many tumors. The majority of tumor cells in oligodendroglial tumors were vimentin negative, except for some of the large polymorphous oligodendrogliomas which contained intermingled vimentin positive glioma cells. GFAP immunoreactivity was detectable only in a low fraction of tumor astrocytes and in a few exceptional cases some oligodendroglial tumor cells stained positive. Immunohistochemistry with antibodies against neurofilaments and cytokeratins revealed no staining in tumor cells of ENU-induced gliomas, while all oligodendrogliomatous tumors stained positive for HNK-1. Immunocytological and immunoblot investigations of the two rat glioma cell clones RG2 and F98, which are both derived from ENU-induced gliomas, showed a prominent expression of vimentin in monolayer cultures and in syngeneic intracerebral transplantation tumors. F98 additionally demonstrated a fraction of GFAP positive cells especially in confluent cultures and in intracerebral tumors. RG2, on the other hand, exhibited virtually no GFAP immunoreactivity in culture but showed individual GFAP positive tumor cells in intracerebral tumors. Our results revealed a more precise picture of the cellular differentiation in ENU-induced rat gliomas and in two widely used glioma cell lines. They underline the heterogeneity of experimental rat gliomas which may comprise cells at different stages of differentiation towards oligodendroglial or astroglial phenotype.